The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A064237 Numbers n such that n! + 1 is divisible by a square. 6
 4, 5, 7, 12, 23, 229 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 229 is another term because 613^2 divides 229!+1. See A115091 for primes whose square divides m!+1 for some m. An examination of the factorizations of m!+1 for m<=100 found no additional squares. - T. D. Noe, Mar 01 2006 562 is also a term because 562!+1 is divisible by 563^2. - Vladeta Jovovic, Mar 30 2004 Comment from Francois BRUNAULT, Nov 23 2008: A web search reveals that for 1 <= n <= 228 there are 82 values of n for which n! + 1 has not been completely factored (the smallest is n=103), so showing that 229 and 562 are indeed the next two terms will be a huge task. I checked that n!+1 is not divisible by p^2 for n <= 1000 and prime p < 10^8. It is very likely that 229 and 562 are the next two terms, but this has not yet been proved. - Nov 29 2008 Contains A007540(n)-1 for all n.  That sequence is conjectured to be infinite. - Robert Israel, Jul 04 2016 This sequence includes A146968 (solutions of Brocard's problem). -  Salvador Cerdá, Mar 08 2016 I may be wrong, but perhaps it is not yet proved that there are no terms between 23 and 228? - N. J. A. Sloane, Jul 24 2017 LINKS Hisanori Mishima, Factorizations of m!+1 EXAMPLE 4 is in the sequence because 4! + 1 = 5^2. 5 is in the sequence because 5! + 1 = 11^2. 6 is not in the sequence because 6! + 1 = 721 7 is in the sequence because 7! + 1 = 71^2. 12 is in the sequence because 12! + 1 = 13^2 * 2834329. 23 is a term because 23!+1 =47^2*79*148139754736864591. 229 and 562 are terms because 229!+1 = 613^2 * 38669 * 1685231 * 3011917759 * (417-digit composite) 562!+1 = 563^2 * 64467346976659839517037 * (1275-digit composite) MAPLE remove(t -> numtheory:-issqrfree(t!+1), [\$1..50]); # Robert Israel, Jul 04 2016 MATHEMATICA Flatten[Position[MoebiusMu[Range!+1], 0]]; (* T. D. Noe, Mar 01 2006, Nov 21 2008 *) PROG (PARI) lista(nn) = for(n=1, nn, if(!issquarefree(n!+1), print1(n, ", "))); \\ Altug Alkan, Mar 08 2016 CROSSREFS Cf. A007540 (Wilson primes), A115091, A146968, A038507, A085692. Sequence in context: A138920 A309833 A048224 * A139373 A293757 A275273 Adjacent sequences:  A064234 A064235 A064236 * A064238 A064239 A064240 KEYWORD nonn,more AUTHOR Vladeta Jovovic, Sep 22 2001 EXTENSIONS Example corrected by T. D. Noe, Nov 26 2008 a(6) from Gionata Neri, Jul 18, 2017 (but see comments) STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 11 08:10 EDT 2021. Contains 342886 sequences. (Running on oeis4.)